We characterized SiO2-TiO2 nano-hybrid particles, prepared using theby sol-gel method, usingwere characterized by high-resolution transmission microscopy (HR-TEM). A few nanometer- ordered TiO2 anatase crystallites could beare observed on the monodispersed SiO2 nanoparticle surface. The quantum size effect of the TiO2 anatase crystallites is attributeds to the blue-shift of the absorption band. The rough surface of the SiO2-TiO2 nano-hybrid particles was derived from the developed growth planes of the TiO2 anatase crystallites, grown from fully hydrolyzed Ti alkoxide that did not non-reacted with acetic acid during the crystallization process atof 600O degree C thermal annealing.

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

The experimental results obtained in this study demonstrated the feasibility of improving the bending strength of rough-ground Si3N4 coated with polymer ceramic precursors and subsequently pyrolyzing the polymer coating. Double coating with 10 mass% polycyclomthylsilazane solution provided the smooth surface, while microcracks were still existence. Increase in the strength of 150MPa was achievable via polymer coating and pyrolyzing while the improvement in the strength variation in terms of the Weibull modulus was insignificant.

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

Defect structures in ZnO have been investigated with a first principle calculation using density functional theory combined with molecular dynamics theory for structural optimization. We calculated formation energy of native defects and impurities in ZnO to explain defect related phenomena observed in ZnO. In particular we paid attention to a deep donor level locating at about 0.3 eV below the bottom of conduction band, which level has been commonly detected in doped and undoped ZnO with deep level transition spectroscopy. From the results for isolated point defects, any possible origin for the deep donor level was not found. However, we found that some impurity complex is likely the origin for the 0.3 eV deep donor levelformed in ZnO.

View full abstract

[in Japanese]

View full abstract

TiO2-based nanomaterials are widely used for pigment and electronics fields, and are recently applied for photocatalysts and dye-sensitized solar cells. Recently, the authors have developed a new direct process to prepare homogeneous titanate and titania nanofibers using natural rutile as a starting material. Since the nanofiber formation and the purification progress in a single-step hydrothermal process, the new process will be more cost-effective and more environmentally friendly than former multi-step processes. In this presentation, processing and some properties of the nanofibers will be reported.

View full abstract

Titanate nanofibers were synthesized by hydrothermal method (150 oC for 72 h) using natural rutile sand as the starting materials. TiO2 (B) and anatase TiO2 (high crystallinity) nanofibers with the diameters of 20-100 nm and the lengths of 10-100 micrometer were obtained by calcined titanate nanofibers for 4 h at 400 oC and 700 oC (in air), respectively.

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

Light is needed to be controlled in "charge separation" or "excitation energy". Nanohybrid sytems are suibale for this purpose, because they can provide new functions that cannot be achieved by a sole molecule nor nanomaterial. Nanohybrid chemistry employing titania nanotube and nano-sized zeolite will be presented.

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

Well-aligned carbon nanotube (CNT) films were synthesized by surface decomposition of silicon carbide (SiC) (000-1). The SiC wafer was heated to 1500˚C at a very small heating rate under vacuum. TEM and electron diffraction patterns revealed that almost all the well-aligned CNTs formed perpendicularly to the SiC (000-1) surface are double-walled and zigzag type. In addition, the results of high-resolution electron microscopy (HREM) indicate that the zigzag-type structure evolves from Si-C hexagonal networks in the SiC crystal by the collapse of carbon layers remaining after the process of decomposition.

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

Metal oxide nanocrystals were precipitated on the sol-gel derived films by hot-water treatment at temperatures lower than 100 ^oC. Additionally, applying of the external reaction fields, e.g., electromagnetic fields, was found to affect the morphologies of the precipitated crystallites. In this study, effects of electric fields on the crystalline growth and the morphologies for the various metal oxides gel films during hot-water treatment were investigated. In addition, relationship between the function of the obtained films and their crystalline morphologies was discussed in detail.

View full abstract

ZnO thin films were deposited by galvanostatic electrolysis with aqueous solution of zinc nitrate. The thinner films with larger electric resistivity were obtained with less current density, though the total deposition terms were set to be equal total charge quantities per substrate area. We presume that the changes were caused by re-dissolution of the films simultaneous with the deposition. In order to control the re-dissolution behaviors, pulsed current was employed. The resistivity of the ZnO films increased by increasing the repetition of the pulse, even though the total charge quantity and total deposition terms were equal. Therefore, it is expected that the defects, such as O vacancy and interstitial Zn, are reduced by using pulsed current and introducing the re-dissolution during depositions.

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

Yttria (Y₂O₃) films were deposited by laser chemical vapor deposition (LCVD) using Y(dpm)₃ (dpm = dipivaloymethanate) precursor. The effect of the total gas pressure (P_tot) on the film morphology was studied. Results showed that the morphology of the yttria film is strongly related to the total gas pressure (P_tot). At lower total gas pressure (P_tot = 0.50 kPa), the deposited films exhibited a columnar microstructure which have a (440) preferred orientation. The surface of the film has a faceted morphology. For higher total gas pressures (P_tot = 1.20 - 2.0 kPa), the deposited films were dense and isotropic with no preferred orientation. The surface morphology showed a cauliflower-like microstructure with grain sizes increased with laser power (P_L).

View full abstract

Second-harmonic generation in optically poled tellurite glasses doped with vanadium and rare-earth element has been observed. The optical poling is carried out by using fundamental wave at a wavelength of 1064 nm and second-harmonic wave at 532 nm from a pulsed Nd:YAG laser. The dependence of second-harmonic intensity on the concentration of dopants is examined. It is found that the second-harmonic intensity is enhanced by the co-doping of terbium. We speculate that the vanadium and terbium play a role of positive hole and electron traps, respectively.

View full abstract

[in Japanese]

View full abstract

The coating of conductive polypyrrole (Ppy) on nonconductive ceramic substrates was carried out. Thick, crack-free deposits of alumina powder were formed on the Ppy coated ceramic substrates by electrophoretic deposition (EPD). Adhesion of the deposits to the Ppy surfaces was fairly good. Alumina ceramics with complex shapes were successfully obtained by sintering the deposits together with the substrates in air.

View full abstract

Preparation of oriented AlN bulk ceramics was achieved by slip casting in a high magnetic field. The c-axis of AlN was oriented on a plane perpendicular to the direction of a magnetic field. Bending strength, fracture toughness and the thermal conductivity of the textured AlN depend on the direction of the crystallographic orientation. These results suggest the possibility of the improvement of these properties simultaneously.

View full abstract

Effects of the solution composition on the deposition behavior of SnO₂ precursor by electrolysis of stannate ammoniacal aqueous solution was investigated. When hydrogen peroxide and nitric acid were added to the solution, the electrolysis was promoted and the deposition rate became larger. Tin dioxide films on SUS304 plates were obtained by the electrolysis and then firing at 500C in air.

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract